What's the weather doing this season?

The Growing Degree Days (GDD) figures for Lincoln through March 13th don't make for pretty reading!!

Currently we sit at 686 GDD (base 10, calculated on a daily basis) while the long term average (LTA, 1931 through 2010) to this point in the season is 812.

 Figure showing the growing degree days for Lincoln, Canterbury based on daily calculations at base 10C

December was the only decent month, having a heat accumulation close to that of LTA, but November, January and February were all cooler than LTA to the tune of about 85% of the value.

Rainfall is about aligned with LTA, the current season to March 13 being about 18mm greater than the LTA of 441mm.

Often, we get a nice March and early April after seasons where the early months' temperatures have been lower than average, but so far this doesn't look like it's happening, with the weather patterns seemingly stuck on cool and unsettled.

The Seasonal Forecast for New Zealand (http://www.niwa.co.nz/seasonal-climate-outlook-march-may-2012) indicates they are expecting more winds from the north-east, which for many of the growing regions in New Zealand, which are along the East coast of the country, means cooler temperatures.

When I look back at the pattern of heat accumulation for Lincoln Uni since the 1998-1999 season when I first arrived in Canterbury, this is the coolest season of them all, bar the 2000-2001 vintage. It's also been a remarkably consistently cool season, whereas in other years it tends to be warmer than LTA at first, then cooler nearer to harvest or vice versa.

So what does this mean for vintage? As long as the fruit stays free of disease (which we've been encouraging through an open canopy), we should be all right. Any opportunity to drop off crop that is tailing behind the average in terms of ripening is a good idea, as well as keeping the canopy open so the fruit dries out more quickly and also gets warming by the sun. We also have to hope that the night-time temperatures don't get too low, as this can be a signal for the vines to get ready for winter and start dropping their leaves! We've already had a couple of nights near 3C!

Our own vineyard, in which we're growing Pinot noir (and a bit of Pinot meunier) for sparkling wine is about 10km from the Lincoln Uni vineyard, but we're harvesting very shortly as the fruit is up to 19 Brix. In a season like this, this show the value of site selection (our vineyard is on the Port Hills and protected from the easterly (and cool) winds), good canopy management and end use of the grapes (sparkling wine, so they are harvested earlier). Of course, that isn't saying anything about how easy it is to sell the wine!

I suppose the good news out of all of this bad weather information is that the December temperatures were reasonably warm, which should mean we still have a decent initiation of flower clusters for the 2012-2013 vintage. 

At least we will have a promising potential to work with!!

Frosts in California (and elsewhere!)

I have mentioned frosts before (August 14 and October 17, 2009), but some recent news brings this subject up again.

Early season frost is a big problem in New Zealand, but also in a lot of other growing regions around the world, such as in Ontario, which I've talked about before. The latest news from California, in an article from Western Farm Press, details the aftermath of a couple of frost events on April 8-10 in areas south of San Francisco. Damage estimates suggested that about one-quarter of the 10,500 hectares of grapes in the Paso Robles area will have a crop that won't be commercially worth harvesting.

Any grower worth his weight in quality secateurs should know what the frost risk is when looking to develop a vineyard, and if the risk is perceived as being great enough, some sort of management system will be planned for the development

Results of a severe spring frost - all green tissues of the vine are completely decimated

If the frosts are mild, then passive means, such as having bare soil between the rows in the spring, which will maximise heat accumulation during the day and release at night, can give from 0.5 to 1.0°C protection (of course, careful decision making in site selection is the best means of passive management!).

Active means of management include such things as taking advantage of an inversion layer (where a layer of warm air sits above the cold air at vine level, and which tend to form on still nights with clear skies) and sending up a helicopter to push the warm air down to mix with the cold.

However, if the frosts are very frequent, then installing a permanent system becomes cost effective, such as the wind machines I've already written about, or using water sprinkled over the vines.

A frost fan installed in Central Otago. Plenty of snow-capped mountains around the area!

There are some big differences between the wind and water methods. The movement of air method relies on mixing the warmer air in an inversion layer with the cold air on the ground. This works great unless 1) the inversion layer doesn't have enough warm air to raise the temperature of the cold air to above freezing or 2) there is no inversion layer.

The former is heartbreaking, as you might be successfully fighting off the freezing temperatures, then just before dawn and the temperature rise that comes with it, the inversion layer is all used up and the grape buds freeze.

The latter has the same outcome, but then you don't have to spend all night running around trying to combat the frost!!

In some cases, the conditions are not right for an inversion layer to form, or the cold might be coming in as a mass of freezing air, for example, from nearby hills or mountains that have recently been covered by snow (this appears to be what happened in California recently). In this case, since there is no warm air around, fans and helicopters won't help. However, the application of water to the plants will work for all types of frost events.

The idea behind the application of water is that as water goes from liquid to solid form (freezes) it releases heat (heat of fusion).

So as long as water is freezing on the plants, heat is being released, effectively keeping the temperature at 0°C. Plant tissues can survive this temperature and even a bit lower without damage, so as long as enough water is supplied to always have some in the process of crystallising, the ice, and grape buds or shoots inside, will be kept from temperatures that might damage them.

Two types of post-mounted micro-sprinklers - these use quite a bit less water than the traditional impact-type overhead sprinklers

The down side is that if enough water is not applied, the temperature can continue to decrease, so if the application system breaks, or the water runs out, before the air temperature rises sufficiently, you can lose the new growth.

In the foreground row visible in this picture there is a number of vines where less growth is visible. This is because the sprinkler at the top of the post (centre left in the photo) failed during a frost event, meaning that the vines were not continuously covered with water - thus once the freezing stopped, the temperature of the ice and tissues within dropped to damaging levels. Note that there is a frost fan in the background - the fan isn't able to cover the area that these vines are in, so the sprinklers were put in to provide protection there.

My preference, if I were to plant in an area that was prone to frost events, would be to use water sprinklers. However, in some cases there wouldn't be enough water available for this. Large dams can be build to provide a source of water, but sprinkling even a hectare of ground with water for a decent frost can require up to 40 cubic metres of water per hour depending on the system used!

The concerning thing is that with global changes to climate, we should be prepared for more extreme weather events - in this context, we need to be ready for more severe frosts later in the season. Seeing as how some grape growing regions in New Zealand can have a potentially damaging frost in almost every month of the year (historically, anyway), this isn't good news!!!

Hands up those who thought being a viticulturist was a cushy job!!

Wind Machines

Since I'm here in Ontario for a while, one does get to touring around vineyards (and wineries!) a bit.

In NZ, wind machines are popping up all over the viticultural landscape, as the most common type of frost occurring in the spring are radiation frosts. Something that moves the air can be very effective in avoiding freeze damage to the vines, because in such a frost cold air develops near the ground, but warmer air accumulates on top of that cold air. This is called an inversion layer, with the warm air stacked on top of the cold.

A wind machine sticks up far enough above the ground (say, 10m) to draw this warmer air down and mix it with the colder air. In most cases, there is a significant reservoir of heat in the inversion layer, meaning that the mixed air is warm enough to prevent freezing of the vine tissues for many hours.

Helicopters are also used to mix the cold and warm layers, but if a vineyard is in a location that is hit consistently with frosts, it can be worth the capital cost to buy, install, and maintain the fans.

So in NZ there are a lot of wind machines being put in to help manage spring freeze events, but here in the Niagara region, they are also putting them in. However, spring frosts are not so much of a concern here (due to the general climate and also the location of the vineyards). So why are people investing in these expensive machines?

Here the main problem is freezing temperatures during the dormant season. Grapes can be very hardy plants, surviving very low temperatures (for certain species, this can be down to less than -40 degrees C!), but vinifera vines tend to be more tender, with a critical temperature of around -18C. So if the temperature in a region tends to get lower than this on a regular basis, you had better have some methods to manage the vines to prevent damage!

One method relies on the presence of the inversion layer, which can appear in the middle of winter as well as in the early spring (or autumn). By mixing the air, freezing temperatures low enough to damage dormant vine tissues can be avoided, leading to productive vines the next season. Without some form of protection, crop losses can be 100 percent, with the added burden of having to re-train the vines (if you're lucky) or re-plant them (if you're not lucky!).

I will write on other strategies to avoid winter freeze damage in another post...